The present invention relates generally to external interface circuitry for data processing systems, and more particularly to a controlled interface for coupling an external device to microcomputer systems.
In prior art computer systems, interface circuitry and peripherals have been typically added to such systems by means of buffering interface signals including address, data and control lines. In such systems, the interface circuitry is powered up when the computer system is switched on. Specialized interfaces, such as the RS-232 interface, have also been developed where special devices are required and special data transfer protocols are used. However, none of these prior art computer systems has a controlled interface which is powered up and powered down in an orderly fashion depending on whether an external device or peripheral is present.